Picture coding method and picture decoding method

ABSTRACT

A picture coding method for preventing occurrence of a malfunction includes: an adding step (Step S 203 ) of coding a memory management command for the first picture of a predetermined picture number and adding the coded command to the second picture that is different from the first picture; and a re-adding step (Steps S 205  to S 208 ) of coding the memory management command again and re-adding re-coded command to the section other than the second picture in a coded picture stream VSt. In the re-adding step, re-addition of the memory management command is prohibited when the first picture is not immediately previous in coding order among the pictures of the predetermined picture number included in the coded picture stream VSt.

This is a continuation application of Ser. No. 10/534,014, filed May 5,2005, which is the National Stage of International Application No.PCT/2004/001899, filed Feb. 19, 2004.

TECHNICAL FIELD

The present invention relates to a picture coding method for codingmoving picture signals on a picture-by-picture basis and a picturedecoding method for decoding the coded signals.

BACKGROUND ART

In the age of multimedia which integrally handles audio, video and otherpixel values, existing information media, i.e., newspapers, magazines,televisions, radios, telephones and other means through whichinformation is conveyed to people, have recently come to be included inthe scope of multimedia. Generally, multimedia refers to something thatis represented by associating not only characters but also graphics,voices, and especially pictures and the like together, but in order toinclude the aforementioned existing information media in the scope ofmultimedia, it appears as a prerequisite to represent such informationin digital form.

However, when calculating the amount of information contained in each ofthe aforementioned information media as the amount of digitalinformation, while the amount of information per character is 1˜2 bytes,the amount of information to be required for voice is 64 Kbits or overper second (telephone quality), and 100 Mbits or over per second formoving pictures (current television reception quality), and thus it isnot realistic for the aforementioned information media to handle such anenormous amount of information as it is in digital form. For example,although videophones are already in the actual use via IntegratedServices Digital Network (ISDN) which offers a transmission speed of 64Kbps/s˜1.5 Mbps/s, it is not practical to transmit video shot bytelevision cameras directly through ISDN.

Against this backdrop, information compression techniques have becomenecessary, and moving picture compression techniques compliant withH.261 and H.263 standards suggested by ITU-T (InternationalTelecommunication Union—Telecommunication Standardization Sector) areemployed for videophones, for example. Moreover, according toinformation compression techniques compliant with the MPEG-1 standard,it is possible to store picture information in an ordinary music CD(compact disc) together with sound information.

Here, MPEG (Moving Picture Experts Group) is an international standardon digital compression of moving picture signals, and MPEG-1 is astandard for compressing moving picture signals, namely, televisionsignal information, approximately into one hundredth. Furthermore, sinceMPEG-1 targets for moderate picture quality which can be realized by atransmission speed of about 1.5 Mbps, MPEG-2, which was standardizedwith a view to satisfy requirements for further improved picturequality, allows data transmission of moving picture signals at a rate of2˜15 Mbps.

Under the present situation, MPEG-4 that achieves a higher compressionratio than that of MPEG-1 and MPEG-2, has been standardized by theworking group (ISO/IEC JTC1/SC29/WG11) which has been engaged in thestandardization of MPEG-1 and MPEG-2. A strong error-proof technique hasinitially been introduced to MPEG-4 for not only allowing efficientcoding at a low bit rate but also allowing reduced subjectivedeterioration of image quality even if a transmission line error occurs.Furthermore, ISO/IEC and ITU-T (Joint Video Team (JVT)) are now jointlymaking efforts to standardize ITU H.264|AVC as a next-generation picturecoding method, and Study of FCD (SOFCD) is the latest standard as ofthis point in time (See “Study of Final Committee Draft of Joint VideoSpecification”, Joint Video Team (JVT) of ISO/IEC and ITU-T VCEG,JVT-F100, 15 Feb., 2003).

In H.264|AVC, differently from the conventional moving picture coding,it is possible to select an arbitrary picture as a forward referencepicture from among a plurality of pictures. Here, a picture indicates aframe or a field.

Reference pictures and the like are stored in a memory.

A memory includes a short-term memory and a long-term memory. Ashort-term memory stores a plurality of pictures which have been decodedimmediately previously, and more specifically, it stores referencepictures such as P pictures (forward predictive coded pictures) and Bpictures (bi-predictive coded pictures) in term of MPEG-1 and MPEG-2. Along-term memory is used for storing pictures for a longer time than theshort-term memory.

A short-term memory is usually a FIFO (First-In First-Out) memory, andin order to store a new picture into the short-term memory whose storagearea is full of pictures, the oldest picture among the pictures whichhave been stored in the short-term memory is removed from the memory andthe new picture is stored in that free area after the removal.Therefore, in the case where it is necessary to refer to, for a longtime, the reference picture which is to be removed from the short-termmemory, the reference picture is usually moved in advance from theshort-term memory to the long-term memory for storage. As a result, itbecomes possible to refer to the reference picture for a long time. Thelong-term memory stores the picture in a specified area. Therefore, thepicture stored in that area can be referred to unless the same area isdesignated and overwritten.

Furthermore, decoded pictures are stored in a display memory temporarilybefore being displayed. This display memory has a FIFO structure inwhich the pictures are overwritten in display order from the older one.

Sophisticated memory management is required for using such a memoryefficiently, so a mechanism for managing a memory is incorporated intoH.264|AVC.

Memory management commands used for the above management are as follows,for example:

1. Command to select pictures which can be referred to;

2. Command to release a memory area of a short-term memory where apicture unnecessary as a reference picture for predictive coding isstored;

3. Command to move the picture stored in the short-term memory to thelong-term memory; and

4. Command to release the memory areas for all the pictures andinitialize the information concerning picture decoding.

In picture coding and decoding, a signal that indicates the referencepicture (reference picture indication signal) is necessary forselecting, on a block-by-block basis, a picture with a smallerprediction error as a reference picture from among the pictures whichcan be referred to. It is possible to narrow down the number ofcandidate reference pictures to an appropriate value by selecting inadvance the pictures which can be referred to, and thus to save thenumber of bits of the reference picture indication signal required foreach block.

In the case where the picture is moved from the short-term memory to thelong-term memory, the picture stored in the short-term memory is removedbecause it is useless duplication of the same picture which is stored inboth the short-term memory and the long-term memory.

In the above picture coding method and picture decoding method, thepicture coding apparatus codes the memory management command thatinstructs removal of an unnecessary picture from a memory and the memorymanagement command that instructs moving of a picture from theshort-term memory to the long-term memory, outputs them, and transmitsthem to the picture decoding apparatus, which decodes them. These memorymanagement commands are added to the coded pictures for transmission. Inthe case where the picture added with the memory management command islost due to a transmission error or the like, the ordering of thepictures in the memory cannot be properly reconstructed on the part ofthe picture decoding apparatus, and thus the pictures cannot be decoded.

In consideration of this problem, it is conceivable to transmit thememory management command (MMCO) again. This retransmission of thememory management command allows proper reconstruction of pictureordering in the memory by the retransmitted memory management commandeven if the picture added with the memory management command is lost dueto a transmission error or the like.

Picture numbers are assigned to respective pictures in order to indicatepictures to which memory management commands are applied and pictureswhich have been added with memory management commands in the case wherethe commands are to be retransmitted. These picture numbers indicate thepictures to be managed and the pictures which were initially added withthe memory management commands.

Picture numbers are the numbers assigned in ascending order (codingorder) in a coded picture stream, and also used for deriving the displayorder of pictures in the display memory. It should be noted that thepicture numbers are coded as remainders of a predetermined numberMaxFrameNum because the picture number becomes significantly larger asthe number of pictures increases.

On the other hand, an IDR picture is introduced in order to ensure thateven if the picture rate or the like of a coded picture stream isswitched in the middle of the stream, the subsequent coded picturestream can be properly decoded. This IDR picture is a picture forprohibiting reference to the pictures which are earlier than the IDRpicture, and the memory areas for the pictures are released and theinformation concerning the picture decoding is initialized at the pointin time when this IDR picture is coded. Therefore, the pictures storedin the memory after the coding or decoding of the IDR picture aredifferent from the pictures stored before that. Furthermore, aninitialization command, instead of the IDR picture, is sometimes used.The IDR picture initializes the decoding information of all the picturesincluding the picture numbers, while the initialization commandinitializes only a part of the information (such as the picturenumbers).

In addition, in the case where the coded picture stream is edited,namely, in the case where another coded picture stream is newlygenerated by extracting a part of each of a plurality of coded picturestreams and combining them, inconsistency of the picture numbers or thelike occurs in the combined point (editing point).

However, there is the following problem in the above picture codingmethod and picture decoding method: even if the retransmitted memorymanagement command indicates the picture to be managed using the picturenumber, it is unknown, on the part of the picture decoding apparatuswhich has received the retransmitted memory management command, to whichpicture the memory management command is to be applied, and thus amalfunction is induced.

In other words, since the picture numbers are represented as remaindersof a predetermined number and the picture numbers are initialized to 0by the IDR picture and the initialization command, the same picturenumber is assigned to different pictures. Therefore, it becomesdifficult to specify one picture by the picture number and thus themalfunction is induced.

For example, the display memory allocates a new area required fordisplay of respective pictures by removing the pictures in display orderfrom the earlier one based on the information concerning their displayorder. Once the picture numbers subsequent to the IDR picture or theinitialization command are reset to 0, the information indicating thedisplay order is also initialized. As a result, even if the picturecoding apparatus retransmits the memory management command formanagement of the picture earlier than the IDR picture or the like, amalfunction occurs in the picture decoding apparatus which has receivedthe command because there exists no picture to which the memorymanagement command is to be applied.

The present invention is conceived in view of this problem, and theobject thereof is to provide the picture coding method and the picturedecoding method for preventing occurrence of a malfunction caused byretransmission of a command.

DISCLOSURE OF INVENTION

In order to achieve the above object, the picture coding method of thepresent invention is a picture coding method for generating a codedpicture signal by repeatedly assigning a predetermined set of picturenumbers in coding order to respective pictures included in a movingpicture signal and coding the pictures on a picture-by-picture basis,the method comprising: an adding step of adding a memory managementcommand to a second picture, the memory management command indicatingmanagement of a first picture of a predetermined picture number in amemory, the first picture and the second picture being different fromeach other; and a re-adding step of re-adding the memory managementcommand to a section other than the second picture in the coded picturesignal, wherein the re-adding step includes: a determining substep ofdetermining whether or not the first picture is located immediatelyprevious to the section in coding order, among pictures of thepredetermined picture number which are located earlier than the sectionin the coded picture signal; and a prohibiting substep of prohibitingthe re-addition of the memory management command when it is determinedin the determining substep that the first picture is not locatedimmediately previous to the section.

Accordingly, the picture to be managed under the retransmitted memorymanagement command is always the immediately previous picture.Therefore, the picture decoding apparatus which has obtained thisre-added and retransmitted memory management command can identify theprevious picture as a picture to be managed under that memory managementcommand even if there are a plurality of pictures of the predeterminedpicture number indicated by the memory management command, and thus canprevent occurrence of a malfunction caused by the retransmitted memorymanagement command on the part of the picture decoding apparatus.

Here, in the determining substep, it may be determined whether or notthe first picture is located earlier than a reference point in the codedpicture signal in coding order, and in the prohibiting substep, there-addition of the memory management command may be prohibited when itis determined in the determining substep that the first picture islocated earlier than the reference point. For example, in thedetermining substep, an editing point is handled as the reference point,the editing point being a point at which continuity of the coded picturesignal is lost by editing. Or, in the determining substep, a codedpicture including information that prompts initialization of the memoryis handled as the reference point.

Accordingly, the memory management command for management of the picturewhich is located earlier than the reference point is not retransmitted.Therefore, the picture decoding apparatus which has obtained thisre-added and retransmitted memory management command can handle thepicture which is located later than the reference point as a picture tobe managed under the memory management command, and thus can preventoccurrence of a malfunction caused by applying the memory managementcommand to, for example, the picture which is located earlier than thereference point and has already been deleted.

Furthermore, in order to achieve the above object, the picture decodingmethod of the present invention is a picture decoding method fordecoding a coded picture signal obtained by coding a moving picturesignal on a picture-by-picture basis, using a predetermined set ofpicture numbers which are repeatedly assigned to respective pictures indecoding order, the method comprising: a determining step of determiningwhether or not a memory management command is added to the coded picturesignal, the memory management command indicating management of a pictureof a predetermined picture number in a memory; a selecting step ofselecting a picture which is located immediately previous to the memorymanagement command in decoding order from among pictures of thepredetermined picture number which are located earlier than the memorymanagement command in the coded picture signal, when it is determined inthe determining step that the memory management command is added; and anexecuting step of executing the management indicated by the memorymanagement command on the picture selected in the selecting step.

Accordingly, the memory management command is applied to the immediatelyprevious picture even if there are a plurality of pictures of thepredetermined picture number indicated by the memory management command.Therefore, it becomes possible to handle the same picture as a pictureto be managed on both parts of the picture coding apparatus and thepicture decoding apparatus by having the picture coding apparatusretransmit the memory management command for management of theimmediately previous picture, and thus prevent occurrence of amalfunction caused by the memory management command retransmitted fromthe picture coding apparatus.

It should be noted that the present invention can be realized not onlyas the above-mentioned picture coding method and picture decodingmethod, but also as a picture coding apparatus and a picture decodingapparatus that use these methods, as a recording medium on which a codedpicture stream obtained by the coding by the picture coding method, oras a program that causes a computer to execute each of the steps in thepicture coding method and the picture decoding method. And needless tosay, such a program can be distributed via a recording medium such as aCD-ROM and a transmission medium such as the Internet.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a picture codingapparatus for realizing a picture coding method according to a firstembodiment of the present invention.

FIG. 2A and FIG. 2B are diagrams showing respective pictures used forexplaining the first embodiment of the present invention.

FIG. 3 is a diagram showing respective pictures used for explainingediting of streams in the first embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of the picture codingapparatus in the first embodiment of the present invention for coding amemory management command again based on an IDR picture.

FIG. 5 is a flowchart showing the operation of the picture codingapparatus in the first embodiment of the present invention for coding amemory management command again based on an IDR picture and a judgmentabout whether a picture is the immediately previous one or not.

FIG. 6 is a flowchart showing the operation of the picture codingapparatus in the first embodiment of the present invention for editing acoded picture signal.

FIG. 7 is a flowchart showing the operation of the picture codingapparatus in the first embodiment of the present invention for coding amemory management command again based on an IDR picture, a judgmentabout whether a picture is the immediately previous one or not, and anediting point.

FIG. 8 is a block diagram showing a configuration of a picture decodingapparatus for realizing a picture decoding method in a second embodimentof the present invention.

FIG. 9 is a flowchart showing the operation of the picture decodingapparatus in the second embodiment of the present invention for handlinga memory management command based on a judgment about whether a pictureis the immediately previous one or not.

FIG. 10 is a flowchart showing the operation of the picture decodingapparatus in the second embodiment of the present invention for handlinga memory management command based on an IDR picture and a judgment aboutwhether a picture is the immediately previous one or not.

FIG. 11 is a flowchart showing the operation of the picture decodingapparatus in the second embodiment of the present invention for handlinga memory management command based on an IDR picture, an editing pointand a judgment about whether a picture is the immediately previous oneor not.

FIG. 12A, FIG. 12B and FIG. 12C are diagrams for explaining a storagemedium in a third embodiment of the present invention.

FIG. 13 is a block diagram showing an overall configuration of a contentsupply system in the third embodiment of the present invention.

FIG. 14 is an external view showing an example of a mobile phone in thethird embodiment of the present invention.

FIG. 15 is a block diagram showing a configuration of the mobile phonein the third embodiment of the present invention.

FIG. 16 is a configuration diagram showing a configuration of a digitalbroadcasting system in the third embodiment of the present embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described below usingthe diagrams.

First Embodiment

FIG. 1 is a block diagram showing a configuration of a picture codingapparatus for realizing a picture coding method according to the presentembodiment.

A picture coding apparatus 100 includes a memory information controlunit 101, a short-term memory management unit 102, a long-term memorymanagement unit 103, a non-storage memory management information unit104, a management information coding unit 105, a reference pictureselection unit 106, a storage area designation unit 107, a referencearea designation unit 108, a picture memory 109, a picture decoding unit111, a picture coding unit 110, a variable length coding unit 112, acounter 113, a counter 114 and others.

The reference picture selection unit 106 selects candidate referencepictures based on a priority indication signal Pri and picture typeinformation PT which are inputted from outside, and notifies the memoryinformation control unit 101 of the selection result.

The memory information control unit 101 judges, based on the picturetype information PT, whether either a forward or backward picture can bereferred to or both forward and backward pictures can be referred to.Furthermore, the memory information control unit 101 instructs thereference area designation unit 108 to output the reference picture(s)that corresponds to the judgment result from the picture memory 109 tothe picture coding unit 110.

The picture coding unit 110 codes an input picture signal Vin on apicture-by-picture basis with reference to the reference pictureoutputted from the picture memory 109. The variable length coding unit112 further performs variable length coding on the output from thepicture coding unit 110 and outputs a coded picture stream VSt. In thecase where the coded picture stream VSt is edited, the variable lengthcoding unit 112 also codes the information indicating the editing pointof the edited coded picture stream VSt. The output from the picturecoding unit 110 is decoded by the picture decoding unit 111 so as to bea decoded picture, and stored in the picture memory 109 as a referencepicture.

In this regard, a memory area of the picture memory 109 where thedecoded picture can be stored is determined according to the instructionfrom the storage area designation unit 107. More specifically, thememory information control unit 101 inquires the short-term memorymanagement unit 102 about the memory area of the short-term memory inthe picture memory 109 from which a picture is removed, so as todesignate it. The storage area designation unit 107 instructs thepicture memory 109 to record the decoded picture in the designatedmemory area.

The short-term memory management unit 102 detects an unnecessary picture(which is not referred to) in the short-term memory, and notifies thememory information control unit 101 of the memory management commandthat instructs removal (release of the memory area) of the unnecessarypicture as a picture to be managed. The long-term memory management unit103 notifies the memory information control unit 101 of the memorymanagement command that instructs moving of the picture in theshort-term memory as a picture to be managed to the long-term memory inthe picture memory 109. These memory management commands are coded bythe management information coding unit 105 so as to be a memorymanagement information stream CSt. The memory management commandsincluded in this memory management information stream CSt are added tothe coded picture stream VSt and transmitted to the picture decodingapparatus.

The counter 113 for the short-term memory and the counter 114 for thelong-term memory count the number of codings of the memory managementcommand that instructs removal of an unnecessary picture and the memorymanagement command that instructs moving of the picture in theshort-term memory to the long-term memory.

The non-storage memory management information unit 104 manages whetheror not the memory management command that instructs removal of anunnecessary picture and the memory management command that instructsmoving of the picture in the short-term memory to the long-term memoryhave been coded and added to the picture in the coded picture stream VStwhich is difficult to be decoded and less important. In the case wherethese memory management commands have been added to the less importantpicture, the non-storage memory management information unit 104instructs the memory information control unit 101 to code the memorymanagement commands again and add them to the coded picture stream VSt.

As a result, the picture coding apparatus 100 transmits the above memorymanagement commands multiple number of times when necessary, and thusprevents the memory management commands in the memory managementinformation stream CSt from being lost due to a transmission line error.

Furthermore, at the time of the second or the subsequent transmission(retransmission) of the memory management command, the memoryinformation control unit 101 detects whether or not the picture which isstored in the memory and to which the memory management command is to beapplied (the picture to be managed) has been coded earlier than the IDRpicture, and does not code the memory management command forretransmission if the picture has been coded earlier than the IDRpicture. Also, the memory information control unit 101 detects whetheror not the picture to be managed is the immediately previous picture incoding order among the pictures assigned the same picture number(because the repeated number is assigned), and codes the memorymanagement command for retransmission only if the picture is theimmediately previous one. Furthermore, the memory information controlunit 101 detects whether or not the picture to be managed is earlier incoding order than the editing point in the coded picture stream VSt atwhich the pictures are discontiguous due to editing, and does not codethe memory management command for retransmission if the picture to bemanaged is earlier than the editing point.

Here, the features of the present embodiment will be described.

FIG. 2A is a diagram showing respective coded pictures.

As shown in this FIG. 2A, picture numbers are assigned to respectivepictures in coding order. The picture number goes back to 0 again whenit comes to the predetermined maximum number (15, for example). Thepicture numbers repeat themselves as just described.

It is assumed that a picture to be coded at the current time (a currentpicture to be coded) is a picture A. In the present embodiment, the casewhere a memory management command (MMCO) attached to a picture which hasbeen coded earlier than the picture A is coded again and added to thepoint of the picture A is described as follows.

It is assumed that respective pictures which have been coded earlierthan the picture A are pictures B0, B1 . . . B15, C0, C1 C11. Thepicture numbers for the pictures B0 to B15 are 0 to 15, while thepicture numbers for the pictures C0 to C11 are 0 to 11. The coding orderof the pictures C0, C1 . . . C11 which are assigned the repeated picturenumbers is closer to the picture A than that of the pictures B0, B1 . .. B15 although they are assigned the repeated picture numbers in thesame manner. Therefore, the picture coding apparatus 100 in the presentembodiment codes again the memory management command to be applied tothe pictures C0, C1 . . . C11, and adds it at the point of the picture Afor transmission, but does not code again the memory management commandto be applied to the pictures B0, B1 . . . B15.

For example, even in the case where a memory management commandindicating that the memory where the picture B2 assigned the picturenumber 2 is stored is to be released (so as to be reusable) has beencoded previously, the picture coding apparatus 100 in the presentembodiment does not code the memory management command again at thepoint of the picture A. Instead, in the case where a memory managementcommand indicating that the memory area where the picture C2 assignedthe picture number 2 is stored is to be released has been codedpreviously, it codes the memory management command again at the point ofthe picture A (re-adds the command to the picture A).

By doing so, when decoding a memory management command that instructsrelease of a memory area, the picture decoding apparatus can determineuniquely which memory should be released, the memory where the pictureB2 of the picture number 2 is stored or the memory where the picture C2of the same picture number 2 is stored. In other words, the picturedecoding apparatus can designate the memory area where the picture C2,which has been coded at the closest time to the current picture A, isstored, as a memory area to be released. As a result, there is nooccurrence of inconsistency of memory status between the picture codingapparatus and the picture decoding apparatus, and thus it is possible toprevent occurrence of malfunctions in the picture decoding apparatuscaused by retransmission of a memory management command.

Another feature of the present embodiment will be explained.

FIG. 2B is a diagram showing respective pictures in the case where thepicture C4 in FIG. 2A is an IDR picture.

An IDR picture is a picture introduced for ensuring that a coded picturestream VSt can be properly decoded even if the decoding of the codedpicture stream VSt is started at the point of the IDR picture, or thestream subsequent to the IDR picture can be properly decoded even if thepicture rate of the coded picture stream VSt is switched just before theIDR picture. This IDR picture prohibits reference to the picturesearlier than the IDR picture, and the memory areas in the memory for allthe pictures are released and the information concerning the decodingthereof is initialized at the point in time when this IDR picture iscoded.

The present embodiment is configured so that, in the case where a memorymanagement command (MMCO) attached to the picture which has been codedearlier than the picture A which is to be currently coded is coded againand added at the point of the picture A, the memory management commandto be applied to the picture is not coded again if the picture has beencoded earlier than the IDR picture.

For example, in the case where the memory management command indicatingthat the memory where the picture C1, which is earlier than the pictureC4 that is an IDR picture, is stored is to be released (so as to bereusable) has been previously coded, the picture coding apparatus 100 inthe present embodiment does not code that memory management commandagain.

The IDR picture initializes the pictures stored in the memory at thispoint in time and their picture numbers. Therefore, in the case where apicture to be managed under a memory management command to beretransmitted is earlier than the IDR picture, there has already been nosuch picture to be managed under the memory management command in thememory of the picture decoding apparatus at the point in time when thememory management command is retransmitted. In such a situation, amalfunction may occur in the picture decoding apparatus, such as newlygenerating the picture which has been lost and storing it into thememory by regarding the situation as an error, and as a result, losinganother picture in the memory.

Therefore, the picture coding apparatus 100 in the present embodimentcan prevent occurrence of such a malfunction by not coding again thememory management command which is to be applied to the picture whichhas been coded earlier than the IDR picture.

Still another feature of the present embodiment will be explained usingFIG. 3.

FIG. 3 is a diagram for explaining editing of coded picture streams VSt.

For example, as shown in FIG. 3, a coded picture stream includingpictures E0 to E13 and a coded picture stream including pictures F0 toF13 are combined with each other (edited) in the middle of therespective streams. It should be noted that coded picture streams areedited in this manner for editing pictures recorded on a DVD or thelike.

The coded picture stream including the pictures E0 to E13 is separatedbetween the picture E11 and the picture E12, while the coded picturestream including the pictures F0 to F13 is separated between the pictureF11 and the picture F12. The coded picture stream including the picturesE0 to E11 and the coded picture stream including the pictures F12 andF13 are combined so as to be edited as a single coded picture stream Y.The point at which the picture numbers are discontiguous as a result ofcombining two streams at the point between the picture E11 and thepicture F12 is called an editing point H.

In order to code again the memory management command (MMCO) attached tothe picture which has been coded earlier than the current picture to becoded, namely, the picture F13, so as to attach it to the picture F13,the picture coding apparatus 100 in the present embodiment determineswhether or not the picture to be managed under the memory managementcommand is a picture which has been coded earlier than the editing pointH. If it is the picture which has been coded earlier than the editingpoint H, the picture coding apparatus 100 prohibits the re-coding of thememory management command.

For example, in the case where the memory management command indicatingthat the memory where the picture F1 that is earlier than the editingpoint H is stored is to be released (so as to be reusable) has beenpreviously coded together with the picture F10 of the picture numberm-2, the picture coding apparatus 100 does not code the memorymanagement command again.

More specifically, since the coded picture stream including the pictureF13 is now the coded picture stream Y after editing, the pictures F0 toF11 which are earlier than the editing point H are not stored in thememory. So, once the memory management command which is applied to anyof the pictures F0 to F11 that are the pictures earlier than the editingpoint H is coded again, the picture decoding apparatus may perform amalfunction of newly generating the lost picture and storing it into thememory and deleting another picture because the picture to which thememory management command is to be applied has been lost when executingthe memory management command. Therefore, the picture coding apparatus100 in the present embodiment prohibits re-coding of such a memorymanagement command.

Here, the operation of the picture coding apparatus 100 in the presentembodiment will be explained.

FIG. 4 is a flowchart showing the operation of the picture codingapparatus 100 in the present embodiment for coding a memory managementcommand again based on an IDR picture.

First, the picture coding unit 110 in the picture coding apparatus 100starts coding the input picture signal Vin (Step S100). The short-termmemory management unit 102 and the long-term memory management unit 103search for unnecessary areas in the memory (pictures which are not to bereferred to for future coding) during the coding processing by thepicture coding unit 110 (Step S101), and determine whether there isunnecessary memory areas or not. Here, when the short-term memorymanagement unit 102 and the long-term memory management unit 103determine that there is unnecessary memory areas (Yes in Step S102), themanagement information coding unit 105 in the picture coding apparatus100 codes the memory management command that instructs release of theunnecessary memory areas (Step S103). Then, the short-term memorymanagement unit 102 and the long-term memory management unit 103 releasethe unnecessary areas (Step S104). When the short-term memory managementunit 102 and the long-term memory management unit 103 determine thatthere is no unnecessary memory area (No in Step S102), the picturecoding apparatus 100 does not execute the operations of Steps S103 andS104.

Next, the memory information control unit 101 determines, based on theoperation of the non-storage memory management information unit 104,whether or not the memory management command that instructs release ofan unnecessary memory area has been coded and added to a previouslycoded picture (a picture earlier than the current picture to be coded)(Step S105), and when it determines that the memory management commandhas not yet been coded (No in Step S105), the picture coding apparatus100 ends the processing.

On the other hand, when it determines that the memory management commandhas been coded (Yes in Step S105), the memory information control unit101 determines whether or not the picture to be managed under the memorymanagement command (the picture which has been stored in the releasedunnecessary memory area) is earlier than the IDR picture in coding order(Step S106). Here, when determining that the picture to be managed isearlier than the IDR picture (Yes in Step S106), the memory informationcontrol unit 101 ends the processing without coding (adding) the memorymanagement command again. When determining that the picture to bemanaged is not earlier than the IDR picture (No in Step S106), thememory information control unit 101 codes (adds) the memory managementcommand again (Step S107), and then ends the processing.

FIG. 5 is a flowchart showing the operation of the picture codingapparatus 100 in the present embodiment for coding a memory managementcommand again based on an IDR picture and a judgment about whether apicture is the immediately previous one or not.

The picture coding apparatus 100 first executes the same operations(S200 to S206) as Steps S100 to S106 as shown in FIG. 4.

When determining that the picture to be managed under the memorymanagement command is not earlier than the IDR picture (No in StepS206), the memory information control unit 101 further determineswhether or not the picture to be managed is the immediately previouspicture among the pictures assigned the picture number same as that ofthe picture to be managed (Step S207). More specifically, the memoryinformation control unit 101 determines whether or not the picture to bemanaged, among the pictures assigned the picture number same as that ofthe picture to be managed, is immediately previous to, in coding order,the point of the coded picture stream VSt at which the memory managementcommand is to be added again.

As a result, when determining that the picture is not the immediatelyprevious one (No in Step S207), the memory information control unit 101ends the processing without coding the memory management command again.When determining that the picture is the immediately previous one (Yesin Step S207), the memory information control unit 101 codes the memorymanagement command again (Step S208) and ends the processing.

FIG. 6 is a flowchart showing the operation of the picture codingapparatus 100 in the present embodiment for editing a coded picturesignal.

First, the picture coding apparatus 100 edits the coded picture streamVSt (Step S300).

Next, the memory information control unit 101 of the picture codingapparatus 100 determines whether or not the memory management commandhas been coded and added to the edited coded picture stream VSt (StepS301).

Here, when determining that the memory management command has been coded(Yes in Step S301), the picture coding apparatus 100 further determineswhether or not the picture to be managed under the memory managementcommand is earlier than the editing point in coding order (Step S302).

On the other hand, when determining that the memory management commandhas not yet been coded in Step S301 (No in Step S301) or whendetermining that the picture to be managed is earlier than the editingpoint in Step S302 (Yes in Step S302), the picture coding apparatus 100ends the processing for editing the coded picture stream VSt.

Furthermore, when determining that the picture to be managed is notearlier than the editing point in Step S302 (No in Step S302), thememory information control unit 101 in the picture coding apparatus 100causes the management information coding unit 105 to code the memorymanagement command again and add it to the coded picture stream VStagain (Step S303).

FIG. 7 is a flowchart showing the operation of the picture codingapparatus 100 in the present embodiment for coding a memory managementcommand again based on an IDR picture, a judgment about whether apicture is the immediately previous one or not, and an editing point.

The picture coding apparatus 100 first executes the same operations(Steps S400 to S407) as Steps S200 to S207 as shown in FIG. 5.

When determining that the picture to be managed under the memorymanagement command is not the immediately previous picture (No in StepS407), the memory information control unit 101 ends the processing. Whendetermining that the picture to be managed is the immediately previousone (Yes in Step S407), the memory information control unit 101 furtherdetermines whether or not the picture to be managed under the memorymanagement command is earlier than the editing point in coding order(Step S408).

When determining that the picture is earlier than the editing point (Yesin Step S408), the memory information control unit 101 ends theprocessing. When determining that the picture is not earlier than theediting point (No in Step S408), the memory information control unit 101codes (adds) the memory management command again (Step S409), and endsthe processing.

As described above, in the present embodiment, the memory managementcommand that instructs release of a memory area (to remove the picturestored in that memory area) is coded repeatedly. Therefore, even if onememory management command is lost due to a transmission line error,another memory management command delivers the instruction of the lostcommand to the picture decoding apparatus, and thus the picture decodingapparatus can decode the picture properly in spite of the transmissionline error.

Furthermore, the picture coding apparatus 100 in the present embodimentdoes not code the memory management command again in the case where thepicture to be managed under the memory management command is earlierthan the editing point, earlier than the IDR picture, or not theimmediately previous picture. Therefore, it is possible to prevent themalfunctions in the picture decoding apparatus caused by the reasonsthat there exists no picture to be managed under the memory managementcommand when the memory management command is executed and the like.

It should be noted that although the present embodiment is describedtaking the memory management command that instructs release of anunnecessary memory area as an example, it may be another memorymanagement command that instructs moving of a picture stored in theshort-term memory to the long-term memory if only it indicates how tomanage the picture in the memory.

In addition, although, in the present embodiment, it is prohibited toretransmit the memory management command when the picture to be managedunder the memory management command is earlier than the IDR picture incoding order, the retransmission may be prohibited when the picture tobe managed is earlier than the memory initialization command in codingorder. This memory initialization command is a command that instructsinitialization of a memory by deleting all the pictures stored in thememory and resetting of the picture number to 0.

Furthermore, although the flowchart in FIG. 7 is explained on theassumption that the picture coding apparatus 100 executes all the StepsS406, S407 and S408 in this order, these steps may be executed in noparticular order, namely, the execution order of the steps may bechanged, or a part of the steps may be omitted for simple realization.

Furthermore, although the flowcharts in FIG. 4 to FIG. 7 show theexample where the memory management command not to be retransmitted iscoded prior to the memory management command to be retransmitted, theymay be coded the other way around, namely, the memory management commandnot to be retransmitted may be coded after coding the memory managementcommand to be retransmitted.

Second Embodiment

Next, the second embodiment of the present invention will be described.

FIG. 8 is a block diagram showing a picture decoding apparatus forrealizing a picture decoding method in the second embodiment.

The picture decoding apparatus 200 includes a memory information controlunit 201, a short-term memory management unit 202, a long-term memorymanagement unit 203, a management information decoding unit 205, astorage area designation unit 207, a reference area designation unit208, a picture memory 209, a picture decoding unit 210, a variablelength decoding unit 212 and others.

The memory information control unit 201 judges based on the picture typeinformation PT whether or not a current picture to be decoded can referto either a forward or a backward picture or both the forward andbackward pictures. The memory information control unit 201 furtherinstructs the reference area designation unit 208 to output thereference picture(s) that corresponds to the judgment result from thepicture memory 209 to the picture decoding unit 210.

The variable length decoding unit 212 performs variable length decodingon the coded picture stream VSt. The picture decoding unit 210 furtherdecodes the output from the variable length decoding unit 212 to outputthe decoded picture signal Vout, and stores the output into the picturememory 209 as a reference picture.

At this time, the memory area of the picture memory 209 where thereference picture can be stored is determined according to theinstruction from the storage area designation unit 207. Morespecifically, the memory information control unit 201 inquires theshort-term memory management unit 202 so as to designate the memory areaof the short-term memory in the picture memory 209 from which thepicture is removed. The storage area designation unit 207 instructs thepicture memory 209 to record the reference picture in the designatedmemory area.

The editing detection unit 215 detects the editing point on the codedpicture stream VSt based on the output from the variable length decodingunit 212, and outputs the information indicating the editing point tothe memory information control unit 201.

The management information decoding unit 205 decodes the memorymanagement information stream CSt, and notifies the short-term memorymanagement unit 202, through the memory information control unit 201, ofthe memory management command that instructs removal of an unnecessarypicture (which is not referred to) in the short-term memory. Themanagement information decoding unit 205 further notifies the long-termmemory management unit 203 of the memory management command thatinstructs moving of the picture stored in the short-term memory to thelong-term memory in the picture memory 209.

Here, if the picture to be managed under the retransmitted memorymanagement command is earlier than the IDR picture in decoding order,the memory information control unit 201 disables the memory managementcommand. If the picture to be managed under the memory managementcommand is earlier than the editing point in decoding order, the memoryinformation control unit 201 disables the memory management command. Andthe memory information control unit 201 regards the immediatelypreviously decoded picture as a picture to be managed, among thepictures assigned the picture number same as the number indicated by thememory management command, and applies the management indicated by thememory management command to that picture to be managed.

The features of the picture decoding apparatus in the present embodimentas described above will be explained using FIG. 2B used in the firstembodiment.

For example, in the case where the decoded memory management command isthe retransmitted one and instructs release of the memory area (so as tomake it reusable) where the picture (C1, for example) which has beendecoded earlier than the IDR picture (C4) is stored, the picturedecoding apparatus 200 disables this memory management command. In otherwords, the picture decoding apparatus 200 does not execute themanagement of the picture C1 instructed by this memory managementcommand.

The IDR picture initializes the pictures stored in the memory at thistime of decoding of that IDR picture. Therefore, in the case where thepicture to be managed under the retransmitted memory management commandis earlier than the IDR picture, there has been no such picture to bemanaged under the memory management command in the memory of the picturedecoding apparatus at the point in time when the retransmitted memorymanagement command is executed. In such a situation, a malfunction mayoccur in the picture decoding apparatus, such as newly generating thepicture which has been lost and storing it into the memory by regardingthe situation as an error, and as a result, losing another picture inthe memory.

Against the backdrop, even if the memory management command for thepicture which has been decoded earlier than the IDR picture isretransmitted, the picture decoding apparatus 200 in the presentembodiment does not execute the management indicated by the memorymanagement command by regarding the retransmission of the memorymanagement command as an error. Therefore, it becomes possible toprevent the above-mentioned malfunction.

Since the picture coding apparatus 100 in the first embodiment generatesa coded picture stream so that above-mentioned memory management commandis not retransmitted, even the conventional picture decoding apparatuscan decode this coded picture stream without causing the abovemalfunction. However, the conventional picture decoding apparatus failsto function normally as mentioned above when decoding the coded picturestream generated by the conventional picture coding apparatus. On theother hand, the picture decoding apparatus in the present embodiment candecode even the coded picture stream generated by the conventionalpicture coding apparatus without causing the malfunction.

Other features of the present embodiment will be explained.

The picture decoding apparatus 200 in the present embodiment applies theretransmitted memory management command to the immediately previouslydecoded picture among the pictures assigned the picture number same asthe picture number of the picture to be managed under the memorymanagement command. This operation of the picture decoding apparatus hasto be coincided with the operation of the picture coding apparatus.Therefore, even in the case where the picture coding apparatus 100 inthe first embodiment prohibits the retransmission of the memorymanagement command for another picture than the immediately previouspicture to be managed so as to generate the coded picture stream, theoperations in the present embodiment have to be executed.

The features of the above-mentioned picture decoding apparatus 200 inthe present embodiment will be described using FIG. 2A used in the firstembodiment.

In the case where the decoded memory management command has beenretransmitted and instructs release of the memory area where the pictureof the picture number 2 is stored, the picture decoding apparatus 200releases the memory area where the picture C2, which is closest to thecurrent time in decoding order, is stored, and does not release thememory where the picture B2 is stored.

Therefore, when decoding the memory management command that indicates torelease the memory area where the picture of the picture number 2 isstored, the picture decoding apparatus 200 in the present embodimenteasily determines which one of the memory areas, where the picture B2and the picture C2 which are assigned the same picture number 2 arerespectively stored, should be released. More specifically, the picturedecoding apparatus 200 can identify the memory area where the pictureC2, which has been decoded at the time closest to the current picture Ato be decoded, is stored, as a memory area to be released. Here, thepicture C2 is the immediately previous picture in decoding orderindicated by the retransmitted memory management command, among thepictures of the picture number 2.

If the picture to be managed under the retransmitted memory managementcommand has been decoded earlier than the editing point, the picturedecoding apparatus 200 in the present embodiment does not apply thismemory management command to that picture.

This characteristic operation of the picture decoding apparatus 200 inthe present embodiment will be explained using FIG. 3.

In the case where the decoded memory management command has beenretransmitted and the picture stored in the memory to which the memorymanagement command is to be applied has been decoded earlier than theediting point H, the picture decoding apparatus 200 does not execute themanagement indicated by that memory management command.

For example, in the case where the decoded memory management command isa retransmitted memory management command and indicates to release thememory area where the picture F1 which is earlier than the editing pointH is stored, the picture decoding apparatus 200 does not execute therelease of the memory area.

More specifically, since the coded picture stream including the pictureF13 is now a coded picture stream Y after editing, the pictures F0 toF11 which are earlier than the editing point H are not stored in thememory. So, if the picture decoding apparatus executes the memorymanagement command which is to be applied to the pictures F0 to F11which are earlier than the editing point H, it may cause a malfunctionof newly generating the lost pictures and storing them into the memoryand deleting other pictures from the memory, because there exists nosuch picture to be managed in the memory when executing that memorymanagement command for that picture. In addition, if there existsanother picture assigned the same picture number as a picture to bemanaged in the memory when executing the memory management command, thememory management command is applied, as an error, to the picture towhich the command should not be applied originally (which is notoperated under the memory management command), and thus there is apossibility that the pictures subsequent to the editing point in thecoded picture stream cannot be properly decoded. Therefore, the picturedecoding apparatus 200 in the present embodiment does not execute thememory management command which is to be applied for management to thepicture earlier than the editing point.

Here, the operation of the picture decoding apparatus 200 in the presentembodiment will be explained.

FIG. 9 is a flowchart showing the operation of the picture decodingapparatus 200 in the present embodiment for handling a memory managementcommand based on a judgment about whether a picture is the immediatelyprevious one or not.

First, the management information decoding unit 205 in the picturedecoding apparatus 200 decodes the memory management command included inthe memory management information stream CSt (Step S500). In this stepof decoding the memory management command (Step S500), the managementinformation decoding unit 205 decodes both the retransmitted memorymanagement command and the memory management command which has beenreceived for the first time (which has not yet been retransmitted).Next, the variable length decoding unit 212 and the picture decodingunit 210 decode the coded picture stream VSt (Step S501).

Next, the memory information control unit 201 determines whether or notthe decoded memory management commands include a retransmitted memorymanagement command (for example, a memory management command thatinstructs release of an unnecessary memory) (Step S502). Whendetermining that there is no retransmitted memory management command (Noin Step S502), the memory information control unit 201 executes anothernon-retransmitted memory management command (Step S503). On the otherhand, when determining that there is a retransmitted memory managementcommand (Yes in Step S502), the memory information control unit 201executes the retransmitted memory management command on the immediatelyprevious picture in decoding order, among the pictures assigned thepicture number same as the picture number indicated by that memorymanagement command (Step S504). More specifically, the memoryinformation control unit 201 executes the memory management command onthe picture which is immediately previous to the memory managementcommand, among the pictures assigned the same picture number andincluded in the coded picture stream VSt earlier than the memorymanagement command in decoding order.

FIG. 10 is a flowchart showing the operation of the picture decodingapparatus 200 in the present embodiment for handling a memory managementcommand based on an IDR picture and a judgment about whether a pictureis the immediately previous one or not.

The picture decoding apparatus 200 executes the same operations (StepsS600 to S603) as Steps S500 to S503 as shown in FIG. 9.

When determining in Step S602 that there is a retransmitted memorymanagement command (Yes in Step S602), the memory information controlunit 201 in the picture decoding apparatus 200 determines whether or notthe picture to be managed under the retransmitted memory managementcommand is a picture which has been decoded earlier than the IDR picture(Step S604). In the case where the retransmitted memory managementcommand is a command that instructs release of an unnecessary memoryarea (so as to be reusable), for example, the picture to be managedunder the retransmitted memory management command means a picture whichis stored in the unnecessary memory area to be released.

Here, when determining that the picture to be managed is earlier thanthe IDR picture (Yes in Step S604), the memory information control unit201 ends the processing without executing the retransmitted memorymanagement command. On the other hand, when determining that the pictureis not earlier than the IDR picture (No in Step S604), the memoryinformation control unit 201 executes the memory management command onthe immediately previous picture in decoding order, among the picturesassigned the picture number same as the picture number indicated by theretransmitted memory management command (Step S605), and ends theprocessing.

FIG. 11 is a flowchart showing the operation of the picture decodingapparatus 200 in the present embodiment for handling a memory managementcommand based on an IDR picture, an editing point and a judgment aboutwhether a picture is the immediately previous one or not.

The picture decoding apparatus 200 executes the operations (Steps S700to S704) same as Steps S600 to S604 as shown in FIG. 10.

When determining in Step S704 that the picture to be managed under theretransmitted memory management command is not earlier than the IDRpicture in decoding order (No in Step S704), the memory informationcontrol unit 201 in the picture decoding apparatus 200 furtherdetermines whether or not the picture to be managed is earlier than theediting point in decoding order (Step S705). More specifically, thememory information control unit 201 determines whether or not thepicture to be managed is a picture which has been decoded earlier thanthe editing point.

Here, when determining that the picture to be managed is earlier thanthe editing point (Yes in Step S705), the memory information controlunit 201 ends the processing without executing the retransmitted memorymanagement command. On the other hand, when determining that the pictureis not earlier than the editing point (No in Step S705), the memoryinformation control unit 201 executes the memory management command onthe immediately previous picture in decoding order, among the picturesassigned the picture number same as the picture number indicated by theretransmitted memory management command (Step S706), in the same manneras Step S504 as shown in FIG. 9, and ends the processing.

As described above, in the case where the picture to be managed underthe retransmitted memory management command is earlier than the editingpoint or the IDR picture, the picture decoding apparatus 200 in thepresent embodiment does not apply (execute) the memory managementcommand. Therefore, it becomes possible to prevent occurrence of amalfunction caused by no existence of the picture to be managed underthe memory management command.

Since the picture decoding apparatus 200 in the present embodimentapplies the memory management command to the picture immediatelyprevious to the current picture to be decoded, among the pictures whichare assigned the same picture number, it is possible to identify thepicture to be managed without fail.

It should be noted that although the present embodiment is described bytaking a memory management command that instructs release of anunnecessary memory as an example, it may be a memory management commandthat instructs moving of a picture stored in the short-term memory tothe long-term memory if only it is a memory management command thatindicates the management of the picture in the memory.

In addition, although, in the present embodiment, it is prohibited toapply a retransmitted memory management command when the picture to bemanaged under the memory management command is earlier than the IDRpicture in coding order, the application thereof may be prohibited whenthe picture to be managed is earlier than the memory initializationcommand in coding order. This memory initialization command is a commandthat instructs initialization of a memory by deleting all the picturesstored in the memory and resetting of the picture number to 0.

Furthermore, although the flowchart in FIG. 11 is explained on theassumption that all the Steps S704, 5705 and S706 are executed in thisorder, these steps may be executed in no particular order, namely, theexecution order of the steps may be changed, or a part of the steps maybe omitted for simple realization.

Third Embodiment

Next, the third embodiment of the present invention will be described.

In the present embodiment, if a program for realizing the picture codingmethod or the picture decoding method as shown in the first or secondembodiment is recorded on a memory medium such as a flexible disk, itbecomes possible to perform the processing as shown in the aboveembodiment easily in an independent computer system.

FIG. 12A to FIG. 12C are illustrations showing the case where thepicture coding method or the picture decoding method in each of theabove embodiments is performed in a computer system using a flexibledisk on which the method is recorded.

FIG. 12B shows a front view of an appearance of a flexible disk, across-sectional view thereof and the flexible disk itself, and FIG. 12Ashows an example of a physical format of the flexible disk as arecording medium body. The flexible disk FD 1 is contained in a case F,and a plurality of tracks Tr are formed concentrically on the surface ofthe disk in the radius direction from the periphery to the inside, andeach track is divided into 16 sectors Se in the angular direction.Therefore, as for the flexible disk storing the above-mentioned program,the program as the picture coding method is recorded in an areaallocated for it on the flexible disk FD.

FIG. 12C shows a structure for recording and reproducing the aboveprogram on and from the flexible disk FD1. When the program as thepicture coding method or the picture decoding method is recorded on theflexible disk FD1, the program is written in the flexible disk from thecomputer system Cs via a flexible disk drive FDD. When the above picturecoding method is constructed in the computer system by the program onthe flexible disk FD1, the program is read out from the flexible diskFD1 using the flexible disk drive FDD and transferred to the computersystem Cs.

The above explanation is made on the assumption that a recording mediumis a flexible disk, but the same processing can also be performed usingan optical disk. In addition, the recording medium is not limited to aflexible disk and an optical disk, but the same processing can beperformed using any other medium such as an IC card and a ROM cassettecapable of recording a program.

The picture coding method and the picture decoding method as shown inthe above embodiments can be implemented, through a semiconductor likeLSI, into a mobile communication device such as a mobile phone and a carnavigation system and a picture-taking device such as a digital videocamera and a digital still camera. Three types of implementations can beconceived: a sending/receiving terminal including both an encoder and adecoder; a sending terminal including an encoder only; and a receivingterminal including a decoder only.

Furthermore, applications of the picture coding method and the picturedecoding method as shown in the above embodiments and systems usingthese methods will be explained.

FIG. 13 is a block diagram showing the overall configuration of acontent supply system ex100 for realizing a content distributionservice. The area for providing communication services is divided intocells of desired size, and base stations ex107˜ex110 that are fixedwireless stations are placed in respective cells.

In this content supply system ex100, devices such as a computer ex111, aPDA (personal digital assistant) ex112, a camera ex113, a mobile phoneex114 and a camera-equipped mobile phone ex115 are connected to theInternet ex 101 via an Internet service provider ex102, a telephonenetwork ex104 and base stations ex107˜ex110.

However, the content supply system ex100 is not limited to theconfiguration as shown in FIG. 13, and any of them may be combined andconnected with each other. Also, each device may be connected directlyto the telephone network ex104, not through the base stationsex107˜ex110 that are fixed wireless stations.

The camera ex113 is a device such as a digital video camera capable ofshooting moving pictures. The mobile phone may be a mobile phone of aPDC (Personal Digital Communications) system, a CDMA (Code DivisionMultiple Access) system, a W-CDMA (Wideband-Code Division MultipleAccess) system or a GSM (Global System for Mobile Communications)system, a PHS (Personal Handyphone System) or the like, and any of themcan be used.

A streaming server ex103 is connected to the camera ex113 via the basestation ex109 and the telephone network ex104, which allows livedistribution or the like using the camera ex113 based on the coded datatransmitted from a user. Either the camera ex113 or the server or thelike for transmitting the data may code the shot data. Also, the movingpicture data shot by a camera ex116 may be transmitted to the streamingserver ex103 via the computer ex111. The camera ex116 is a device suchas a digital camera capable of shooting still and moving pictures. Inthis case, either the camera ex116 or the computer ex111 may code themoving picture data. An LSI ex117 included in the computer ex111 or thecamera ex116 actually performs coding processing. Note that software forcoding and decoding pictures may be integrated into any type of storagemedium (such as a CD-ROM, a flexible disk and a hard disk) that is arecording medium which is readable by the computer ex111 or the like.Furthermore, the camera-equipped mobile phone ex115 may transmit themoving picture data. This moving picture data is the data coded by theLSI included in the mobile phone ex115.

The content supply system ex100 codes contents (such as a live musicvideo) shot by users using the camera ex113, the camera ex116 or thelike in the same manner as the above embodiment and transmits them tothe streaming server ex103, while the streaming server ex103 makesstream distribution of the contents data to the clients at theirrequest. The clients include the computer ex111, the PDA ex112, thecamera ex113, the mobile phone ex114 and so on capable of decoding theabove-mentioned coded data. In the content supply system ex100, theclients can thus receive and reproduce the coded data, and the clientscan further receive, decode and reproduce the data in real time so as torealize personal broadcasting.

When each device in this system performs coding or decoding, the picturecoding apparatus or the picture decoding apparatus, as shown in each ofthe above-mentioned embodiments, can be used.

A mobile phone will be explained as an example of the device.

FIG. 14 is a diagram showing the mobile phone ex115 that uses thepicture coding method and the picture decoding method explained in theabove embodiments. The mobile phone ex115 has: an antenna ex201 forsending and receiving radio waves to and from the base station ex110; acamera unit ex203 such as a CCD camera capable of shooting video andstill pictures; a display unit ex202 such as a liquid crystal displayfor displaying the data obtained by decoding video and the like shot bythe camera unit ex203 and received via the antenna ex201; a body unitincluding a set of operation keys ex204; a voice output unit ex208 suchas a speaker for outputting voices; a voice input unit 205 such as amicrophone for inputting voices; a storage medium ex207 for storingcoded or decoded data such as data of shot moving or still pictures,data of received e-mails, data of moving or still pictures; and a slotunit ex206 for attaching the storage medium ex207 to the mobile phoneex115. The storage medium ex207 includes a flash memory element, a kindof EEPROM (Electrically Erasable and Programmable Read Only Memory) thatis an electrically erasable and rewritable nonvolatile memory, in aplastic case such as an SD ca rd.

The mobile phone ex115 will be further explained with reference to FIG.15. In the mobile phone ex115, a main control unit ex311 for overallcontrolling the display unit ex202 and the body unit including operationkeys ex204 is connected to a power supply circuit unit ex310, anoperation input control unit ex304, a picture coding unit ex312, acamera interface unit ex303, an LCD (Liquid Crystal Display) controlunit ex302, a picture decoding unit ex309, a multiplex/demultiplex unitex308, a record/reproduce unit ex307, a modem circuit unit ex306 and avoice processing unit ex305, and these units are connected to each othervia a synchronous bus ex313.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex310 supplies respective units with powerfrom a battery pack, so as to activate the camera-equipped digitalmobile phone ex115 for making it into a ready state.

In the mobile phone ex115, the voice processing unit ex305 converts thevoice signals received by the voice input unit ex205 in voiceconversation mode into digital voice data under the control of the maincontrol unit ex311 including a CPU, ROM and RAM or the like, the modemcircuit unit ex306 performs spread spectrum processing of the digitalvoice data, and the send/receive circuit unit ex301 performsdigital-to-analog conversion and frequency transform of the data, so asto transmit it via the antenna ex201. Also, in the mobile phone ex115,after the data received by the antenna ex201 in voice conversation modeis amplified and performed of frequency transform and analog-to-digitalconversion, the modem circuit unit ex306 performs inverse spreadspectrum processing of the data, and the voice processing unit ex305converts it into analog voice data, so as to output it via the voiceoutput unit 208.

Furthermore, when transmitting e-mail in data communication mode, thetext data of the e-mail inputted by operating the operation keys ex204on the body unit is sent out to the main control unit ex311 via theoperation input control unit ex304. After the modem circuit unit ex306performs spread spectrum processing of the text data and thesend/receive circuit unit ex301 performs digital-to-analog conversionand frequency transform for it, the main control unit ex311 transmitsthe resulting data to the base station ex110 via the antenna ex201.

When picture data is transmitted in data communication mode, the picturedata shot by the camera unit ex203 is supplied to the picture codingunit ex312 via the camera interface unit ex303. When the picture data isnot transmitted, it is also possible to display the picture data shot bythe camera unit ex203 directly on the display unit 202 via the camerainterface unit ex303 and the LCD control unit ex302.

The picture coding unit ex312, which includes the picture codingapparatus as explained in the present invention, compresses and codesthe picture data supplied from the camera unit ex203 by the codingmethod used for the moving picture coding apparatus as shown in theabove embodiments so as to transform it into coded picture data, andsends it out to the multiplex/demultiplex unit ex308. At this time, themobile phone ex115 sends out, to the multiplex/demultiplex unit ex308via the voice processing unit ex305, the voices received by the voiceinput unit ex205 during shooting by the camera unit ex203, as digitalvoice data.

The multiplex/demultiplex unit ex308 multiplexes the coded picture datasupplied from the picture coding unit ex312 and the voice data suppliedfrom the voice processing unit ex305 by a predetermined method, themodem circuit unit ex306 performs spread spectrum processing of themultiplexed data obtained as a result of the multiplexing, and thesend/receive circuit unit ex301 performs digital-to-analog conversionand frequency transform on the data for transmission via the antennaex201.

As for receiving data of a moving picture file which is linked to a Webpage or the like in data communication mode, the modem circuit unitex306 performs inverse spread spectrum processing on the data receivedfrom the base station ex110 via the antenna ex201, and sends out themultiplexed data obtained as a result of the processing to themultiplex/demultiplex unit ex308.

In order to decode the multiplexed data received via the antenna ex201,the multiplex/demultiplex unit ex308 separates the multiplexed data intoa bit stream of picture data and a bit stream of voice data, andsupplies the coded picture data to the picture decoding unit ex309 andthe voice data to the voice processing unit ex305 respectively via thesynchronous bus ex313.

Next, the picture decoding unit ex309, which includes the picturedecoding apparatus as explained in the present invention, decodes thebit stream of picture data by the decoding method corresponding to thecoding method as shown in the above-mentioned embodiment to generatereproduced moving picture data, and supplies this data to the displayunit ex202 via the LCD control unit ex302, and thus moving picture dataincluded in a moving picture file linked to a Web page, for instance, isdisplayed. At the same time, the voice processing unit ex305 convertsthe voice data into analog voice data, and supplies this data to thevoice output unit ex208, and thus voice data included in a movingpicture file linked to a Web page, for instance, is reproduced.

The present invention is not limited to the above-mentioned system, andat least either the picture coding apparatus or the picture decodingapparatus in each of the above-mentioned embodiments can be incorporatedinto a system for digital broadcasting as shown in FIG. 16. Suchground-based or satellite digital broadcasting has been in the newslately. More specifically, a bit stream of video information istransmitted from a broadcast station ex409 to a communication orbroadcast satellite ex410 via radio waves. Upon receipt of it, thebroadcast satellite ex410 transmits radio waves for broadcasting, ahome-use antenna ex406 with a satellite broadcast reception setupreceives the radio waves, and a device such as a television (receiver)ex401 or a set top box (STB) ex407 decodes the bit stream forreproduction. The picture decoding apparatus as shown in theabove-mentioned embodiment can be implemented in the reproductionapparatus ex403 for reading off and decoding the bit stream recorded ona storage medium ex402 that is a recording medium such as a CD and DVD.In this case, the reproduced video signals are displayed on a monitorex404. It is also conceived to implement the picture decoding apparatusinto the set top box ex407 connected to a cable ex405 for a cabletelevision or the antenna ex406 for satellite and/or ground-basedbroadcasting so as to reproduce them on a monitor ex408 of thetelevision. The picture decoding apparatus may be incorporated into thetelevision, not into the set top box. Or, a car ex412 having an antennaex411 can receive signals from the satellite ex410, the base stationex107 or the like for reproducing moving pictures on a display devicesuch as a car navigation system ex413 in the car ex412.

Furthermore, the picture coding apparatus as shown in theabove-mentioned embodiments can code picture signals for recording themon a recording medium. As a concrete example, there is a recorder ex420such as a DVD recorder for recording picture signals on a DVD disc ex421and a disk recorder for recording them on a hard disk. They can also berecorded on an SD card ex422. If the recorder ex420 includes the picturedecoding apparatus as shown in the above-mentioned embodiments, thepicture signals recorded on the DVD disc ex421 or the SD card ex422 canbe reproduced for display on the monitor ex408.

As the structure of the car navigation system ex413, the structurewithout the camera unit ex203, the camera interface unit ex303 and thepicture coding unit ex312, out of the units shown in FIG. 15, can beconceived. The same applies to the computer ex111, the television(receiver) ex401 and others.

In addition, three types of implementations can be conceived for aterminal such as the above-mentioned mobile phone ex114; asending/receiving terminal including both an encoder and a decoder, asending terminal including an encoder only, and a receiving terminalincluding a decoder only.

As described above, it is possible to use the picture coding method orthe picture decoding method as shown in each of the above-mentionedembodiments in any of the above-mentioned apparatuses and systems, andusing this method, the effects described in the above embodiments can beobtained.

The present invention is not limited to the above-mentioned embodiments,and various changes and modifications may be made without departing fromthe spirit and scope of the invention.

INDUSTRIAL APPLICABILITY

The picture coding method and the picture decoding method according tothe present invention can prevent occurrence of a malfunction caused byretransmission of a command, and can be applied to a picture codingapparatus such as a video camera and a mobile phone with a recordingfunction for coding pictures by the present picture coding method and apicture decoding apparatus such as a personal computer and a mobilephone for decoding coded signals by the present picture decoding method.

1. A picture decoding LSI that decodes a coded picture signal obtainedby coding a moving picture signal on a picture-by-picture basis, using apredetermined set of picture numbers which are repeatedly assigned torespective pictures in decoding order, the apparatus comprising: adetermining unit operable to determine whether or not a memorymanagement command is added to the coded picture signal, the memorymanagement command indicating management of a picture of a predeterminedpicture number in a memory; a selecting unit operable to select apicture which is located immediately previous to the memory managementcommand in decoding order from among pictures of the predeterminedpicture number which are located earlier than the memory managementcommand in the coded picture signal, when it is determined by thedetermining unit that the memory management command is added; anexecuting unit operable to execute the management indicated by thememory management command on the picture selected by the selecting unit;a reference point determining unit operable to determine whether or nota picture to be managed under the memory management command is locatedearlier than a reference point in the coded picture signal in decodingorder, when it is determined in the determining unit that the memorymanagement command is added; and a management disabling unit operable todisable the management indicated by the memory management command whenit is determined in the reference point determining unit that the firstpicture is located earlier than the reference point.
 2. A mobile phonewhich comprises the LSI of claim 1.